Telephone system



Dec- 28, 1937- N. H. sAuNDE-Rs 2,103,301

A TELEPHONE SYSTEM Filed oet. 21, 1955 .2v sheets-sheet 1 INVENToR. fNoPMA/V H SAUNDERS ATTORNEY.

In. lll- 4Q m23 Saum Dec. 28, 1937, I N, SAUNDERS 2,103,301

TELEPHONE SYS TEM Filed Oct. 21 1955 2 Sheets-Sheet 2 5% l l l 4 Ig l O D Q? 3? 3 20. 2 o E 8 l I l I l l l l I l l l l l l N l l .s l u 3mm, mx, :s 'I y o o o 2 I` n 3 a Q au S551 IN VEN TOR. NORMAN H. SAUNDEPS Patented Dec. 28, 1.937j

UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Norman H. Saunders, Chicago, Ill., assigner to y v Associated Electric Laboratories, Inc., Chicago, if Y -f lil., a corporation of Delaware aspri-reunen october 21, 1935, serial', 10.45.846

9 claims. (ci. 179-16) The present invention relates to telephone munity automatic exchanges. TheA following systems, but concerned more particularly with patents are cited as showing the state of the art: telephone systems which give service to rural 1,502,168, John Wicks ,Ju1y,22, 1924, 1,502,877, A.` communities through the medium of automatic J. Ray, July l29, 1924, and 1,681,015,l N. s vvi hing apparatus. l Saunders, Aug. 14,1928. lhebroad general object of the invention is It is anobject of theinvention to provide a this production of new and improved control cirrepeaterffor the individual use of a rural line,

euitsfor enabling Yautomatic service to be given which automatically adjustsitself to the length more satisfactorily from lines of widely differing of line included when a subscriber is calling, lcliaracteristics. A more specific object of the according to the remoteness ofthe calling sub- 10 invention is the production of a new and imstation. n Y y proved repeater which may be inserted in a A further object of the invention is to provide rural subscriber line to respond to the dialling an individual-line repeater which permits of all impulses generated thereon to repeat satisfactory the services normally provided for in a standard impulses to the switching apparatus. community exchange. A special problem arose j in handling reverting calls while permitting sat- Y 4 Genfer Mmmm isfaetory switch-hook recalling of a Called op- Asis weil known, in many rural communities erator, which problem was solved b-y circuit arand towns, some of the lines radiating from the rangements including a polarized cut-off relay, K telephone exchange are relatively yshort town as will be brought out in detail hereinafter.

lines connecting with nearby subscribers sta- Referring now to the accompanying drawings tions; other lines extend to stations of nearby comprising Figs. 1 and 2, they .show by means rural subscribers; and still other lines extend of the usual circuit diagrams a suihcient amount along ruralroutes to serve subscribers stations of the apparatus involved vin a telephone system located at various distances from the exchange. embodying the invention to enable the invention Because of the variation in line resistance afto be understood. fcrded4 by the different lines entering the ex- Fig. 1 shows the rural-line repeater RLR, inchange,A which* condition is complicated somedividual to the multi-station rural line RL, be-

by the fact that the longer lines usually ing inserted between the called terminals of the 3Q have many substations connected thereto, it is rural line and the individual line circuit LC, FigigKV quite "diflicult to Ysecure an adjustment of the 2,both Yof which are located inthe exchange. line relays of the automatic switching appararl`he rural line RL is also associated with calling tus-.which will enable the apparatus to operate terminals comprising the terminals indicated at. satisfactorily7 from all of the lines of the exthe left-'hand portion of Fig. 2. Three substa- 5 change. .tions (AI, A2, and AN) are shownrconnected 35 ,Although circuit arrangements are known to the line RL. There are assumed to be several which substantially extend the normal range of more.

characteristics of lines over which automatic Fig. 2, in addition to the individual line circuit switching apparatus may be operated, it has LC, shows one finder-connector link composed of so been found in practice that some rural lines imthe nder F and the associated connector C, 40

pose so much more severe impulsing conditions which is one link of a number provided to handle than a majority of the lines that it is often the traffic in the community automatic exchange. economical to provide certain lines with in- Fionafull disclosure of the finder-connector link dividual repeaters. Then the impulse-respondpartially shown in Fig. 2, reference may be had by all lines may be adjusted with special refer- 1935.

enc-e to more nearly normal line characteristics, As pointed outfin my prior patent, each of while the severe conditions imposed by the few the lines is provided with a line circuit such as lines are more or less compensated for by the LC, Fig. 2. Except for a few of the longest lines,

3o respective repeaters individual thereto. or lines in a poorly maintained condition, each 5o Repeaters have been used before individual to line terminates directly in the line conductors of certain rural lines of an exchange. Each of its individual line circuit, as disclosed in my these prior repeaters, however, has proved to be prior patent above referred to. The rural line unsatisfactory in one or more respects in giving RL, however, is assumed to be one of the lines the" service required in modern unattached comwhich presents unusually severe impulsing con- "5- ing. apparatus of the switches used in common to my prior Patent 1,999,788, granted April 30, 45

connected therewith by means of the talking conductors 14| and |42 and the third or control conductor |43.

In order to control the connection of the repeater RLR tothe call terminals there is vassociated with these call terminals switching means in the form of a cut-olf relay |00 which operates.

to disconnect the lineirom the repeater when a subscriber on the line RL is called, thereby to avoid interference during the Detailed description The disclosure having been described Agenerally, a detailed description of the operation of the apparatus disclosed will now be given.

Y Callingrhe rural Zine RL Y Theroperations involved when the rural line RL is called will first be described. It may beV assumed that the finder F has found a calling line and that the connector C has been operated in the usual manner in accordance with the number assigned to the rural line RLandhas been'conditicned to supply ringing-current to signal'a 202 of the line circuitLC and also by way of the upper winding of cut-olf relay |00 of the repeater RLR'. This negative potential marks the rural line RL as idle in the bank of the connector C and the other similar connectors to which the line is multipled.

"Now,"when the rural line RL l connector'C, by way of wipers |82, |85, and |83, ground potential is placed on the C conductor of the line RL through the VC wiper |83 of the connector. When this occurs, cut-oir relay 202 of the Vline circuit LC is operated, but without any particular function at this'time. In addition, the cutoif relay |00vofl the repeaterRLR is operated through thc resistor Il and contacts of relay I2 to disconnectI the talking conductors of the line RL from' therepeater RLR. These two Vcut-off relays remain operated over the`C f conductor of the called line as long as the connection remains established, and cutoif relay V|00 maintains the line RL clearedfrom the repeater, RLR.

Y When the connection is broken down upon theV restoration of theconnector C, Fig. 2,;the re' moval of ground potential from the C conductor of the. called line results in the restoration of the cut-oir relays |00 and 202, thereby returning the circuits Vassociated with the called line to normal condition. f

VAt thisV point it may be mentioned that the cutoif relay |00 Visof the well-known three-pole construction exemplied in Patent 1,673,884, grant,-

edA June 19, 1928, to Harold C. Pye. The lower winding of relay I0 is the one nearest the heelf end of the relay, while the upper winding of the relay" is the one nearest the armature of'the .relay. Y

' Originating a call mt the rural Zine The operations involved in setting up a con-k 5RL extends to ground by Vretard coil |08,

ringing operation. y

is seized by theY cuit in series with line relay |0|.

nection from the rural line RL to a desired other K line will now be described. For this purpose it may be assumed that the subscriber at substation A2 on the rural line RL'removes his receiver, thereby closing a bridge across the conductors of theline. In the exchange, the line RL extends by way of contacts of the normally restored cutolfV relay |00 to theleft-hand windings ofthe repeating coil |||1of the repeater RLR. -The lower left-hand winding of the repeating coil way of the balancing while the upper leftg-hand winding of the repeating coil extends to the negative, `ungrounded pole of the exchange battery Y, by way of line relay I0 I, through contacts of cut- `Vinrelay- |01 Vand the marginal test relay-|05. The purpose Line Vrelay |0| energizes over the calling line when the receiver is removed at substation A2. Upon energizing, it closes aY circuit for release relay |02 at its inner armature, while at its lower armature it closes a circuit for repeating relay ||0 through contacts of timer relay |09. Repeating relay H0 operates and closes a locking circuit for itself at its lower contacts by way of resistor' H3, while at its inner upper armatureit closes the circuit of timer relay |09. Timer relay |09 opens the initialcircuit of repeating relay ||0 at its lower armature, leaving repeating relay H0 operated through resistor ||3 and the lower contacts ofthe relay. 'I'imer relayA |09 also closes a local circuit for its upper winding to render the relay slow releasing, and it closes a multiple circuit for release relay |02;

When release relayl |02 operates, it prepares a priming circuit by way of resistor |`|2 for the line relay.V Release relay |02 also places a second shunt around the lower winding of cut-off relay |00 and disconnects the upper winding of relay |10 to prevent operation of relay |00 when ground potential is retained on the C lead by the line circuit LC. Auxiliary release relay |03 now operates through contacts of release relay |02 and prepares a circuit for series relay |04 at its inner contacts, while at its upper-contacts it removes the normally existing shunt from around the lower winding of cut-off relay |00 for a purpose to be laterV brought out, but at this time a new shunt has been closed around its lower winding at contacts ofrelease relay |02.

kTesting the resistance'af the subscriber loop One of the features of the repeater RLR is that it tests the calling loop to determine whether the 1" current-flow or resistance testv is made by theV marginalV test relay |05, which is normally in cir- When the calling substation is fone located relatively near the exchange, (AI for example)V the current ow is suiicient to operate test relay |05, but when the calling substation is near the end of the line, (AN for` example) Vand the resistance is great as a. result, the current now is, reduced suiliciently that test relay |05 does not operate. When test relay of the marginal test relay |05 will` be discussed subsequently.

|05 does operate, it closes a circuit for cut-in relay |01, from groundat the inner contacts of release relay |02. Cut-in relay |01 thereupon operates and locks itself independent of the contacts of test relay |05. Cut-in relay |01 transfers the circuit of line relay 0| so that it includes the resistor H5 instead of the low resistance test relay |05, thereby increasing the loop resistance to compensate for the low loop resistance alorded by a substation relatively near the exchange.

Takingcn idle Zink for use As a further result of the energization of repeating relay |0 (responsive to the operation of line relay llil), the right-hand windings of ref peating coil IH are bridged across the conductors |4| and |42, leading to the line circuit LC. When this occurs, line relay 20| operates over conductors |4| and |42 and through resistor H0, as the upper winding of line relay 20| is connected bee tween the negative pole of the exchange battery and conductor HH by way of the upper contacts of cut-01T relay 202, and the lower Winding of the line relay is connected between the positive conductor |42 and ground, by way of the lower contaots of the cut-off relay. Upon energizing, line relay 20| disconnects the C conductor |43 from cut-ofi relay 202 and connects it to ground, thereby extending `a guarding potential through the middle contacts oi the operated release relay |02 to the C conductor associated with rural line RL and extending to the connector banks. The lin-e RL is thereby guarded against seizure by the connectors.

As a further result of this operation, the line relay 20| connects the winding of cut-oirelay 202 at its upper contacts through contacts of lockout relay 203 to the C lead extending to the banks of the nder F and the other finders which have access to the line circuit LC, thereby marking the line circuit LC as calling in the nder banks. The line relay 20| also extends ground potential by way of contacts of lockout relay 203 to start conductor 205, thereby causing a nder to be started in the usual manner.

It may be assumed that the finder F is the one which responds to the grounding of start conductor 205, in which case the wipers 5I--53 are' rotated in search of the calling line. When these wipers arrive on the contacts assigned to the line circuit LC, the rotation is stopped by the closure of a test circuit from ground through the C wiper 53 in series with cut-oir relay 202, through the upper contacts of relay 20|. Cut-off relay 202 locks itself to the associated C lead extending to the iinder bank, at the same time disconnecting line relay 20| from in bridge of the talking conductors and closing a circuit for lockout relay 203. Lockout relay 203 now operatesY and remains operated as long as cut-off relay 202 is held operated. Line relay 20| now restores and extends the incoming C conductor H33 through contacts of the operated cut-off relay 202 to the now grounded C lead eX- tending to the finder bank. Start conductor 205 becomes ungrounded upon the operation of lockout relay 203 and the restoration of start relay 20|.

The connector C is now prepared in the usual manner to respond to the digits of the desired number, the operating circuit for the line` relay (not shown) of the connector being over conductors and |42 and through the upper contacts of repeater relay ||0. n

Repeating the digitV impulses When the calling subscriber turns his` calling device in accordance with the firstA digit in the desired number, the calling loop is interrupted one or more times upon the return of the calling device to normal position. Each time the calling loop is interrupted, the resulting cessation of current llow results in the momentary restoration of the line relay |05, and' line relay |0| controls repeating relay H0 to cause the interruptions to be repeated at the upper contacts of the repeating relay into the loopextending to the connector shown in Fig. 2, thereby securing the operation of the connector. Each reoperationof. line relay i0| is assisted and' hastened by the primary circuit closed through'resistor I |2.

' The first time it is restored, the repeating relay v H0 closesa circuit at its inner upper armature through contacts of the operated auxiliary relay |03 for the winding of slow-releasing series relay |04. Series relay |02 places ground potential on the lower talking conductor to remove the lower winding of the repeating coil and the retard coil |00 from circuit in order to lower the impedance of the line during dialling. Series relay |00 also closes a circuit from ground at the inner contacts of release relay |02 -for by-pass relay |00. Bypass relay |06 thereupon operates and closes a locking circuit for itself to maintain it operated after the series relay has restored, and at its upper contacts it lay-passes the marginal test relay |05 so as to remove this relay from circuit after the dialling has begun, whether the associated cutin relay |07 has been operated or not.

Also, when relay H0 restores, it further` dis- A The circuit of the lower winding of timer relay |09 is opened each time repeating relay I0 restores,

` permitting relay |09 to restore at the end of the interval for which it is adjusted. Timer relay-|09 is adjusted to insure at least a minimum'circuit opening at the upper contacts of repeating relay When it finally restores, timer relay |00 again prepares a circuit for repeating relay H0 at its lower armature, thereby again placing relay H0 under the control of line relay IBI. It is to be particularly noted that repeating relay H0 cannot reoperate before timer relay |00 restores, even though the linerelay i0! reoperatesV almost immediately after itrestores, as the repeating relay ||0 disconnects itself as above pointed out when it restores. Y

With timer relay |09 restored, when line relay |0| reoperates (whichever occurs last). a circuit is closed through the lower contacts of relays |0| and |09 for reoperating repeating relay I0. Repeating relay H0 again locks itself through resistor H3; again closes the loop circuit extending to the connector C and it again opens the circuit of series relay |00 and reclosesV the circuit of timer relay |00. Timer relay E09 has the circuit of its upper winding normally open so as to avoid a retardation of the operatingv time of the relay, with the result that the relay reoperates very quickly. Upon the reoperation oftimer relay |00, the initial circuit oi repeating relay H0 is again opened at the lower contacts of the timer relay. The resistor H3 limits the current flow through relay ||0yto a low value so that the relay restores quickly when the circuit of the repeating 7g lower contacts of relay |0l.

By the foregoing arrangement, a minimum line opening is repeated to the connector upon each restoration of line relay |0|, however, momentary, responsive to a break in the calling line at the callingl device, which minimum opening is sufcient to secure satisfactory operation of an operating magnet. It is to be noted that timer relay |09 assists line relay 10| in maintaining slow acting release relay |02 operated throughout impulsing. Y

At the end of the series oi impulses, line relay |0|, repeating relay H0, and timer relay |09 all come to rest in an energized condition. Series relay |04 now restores as its circuit is maintained open at theV contacts of repeating relay H0. Series relay |04 disconnects ground potential from the incoming positive conductor at its upper contacts so as to restore the normal balanced condition to the line, while at its inner contacts it opens the initial circuit of by-pass relay |06, but this relay remains operated at its locking circuit, closed through its inner contacts.

Relays |0|, H0, |09, and |04 reoperate asV described in the repeating of'each subsequently dialled series of impulses. Y

When the connection has been set up by way of the nder F and the connector C to the desired called line, and the called subscriber has responded, conversation may take place in the usual manner.

When the calling subscriber replaces his receiver at the end of the conversatiomrelays |0|, H0, and |09 restore, and repeating relay H0 opens the circuit extending to the impulsing apparatus ofthe connector C. With relays i0| and |09 restored, the holding circuit of release relay |02 is opened and release and auxiliary-release relays |02 and |03 restore successively` Series relay |04, which is operated incidentally through contacts of the restored repeating relay ||0 and contacts of auxiliary relay |03, restores responsive to the restoration of relay |03. By-palss and cut-in relays |06 and |01 are unlocked atL the inner contacts of release relay |02when the circuit of auxiliary release relay |03 is opened.

Responsive to the opening of the control cilcuit at the upper contacts of repeating relayi0, the connector C and the iinder F are permitted to clear out and ground potential is removed from the C lead of theline circuit LC, wherein cutoi relay 202 has been held operated over the C lead, and lock-out relay 203 has been maintained operated through contacts of cut-off relay 202. Cut-ofi relay 202 now restores and permits the slow acting lock-out Yrelay 2013 to restore a moment later, returning the line circuitLC to normal condition. The rural line RL is now marked idle in the connector bank upon the disconnection of ground potential from the C lead thereof and the reapplication of the negative potential to the C lead through thewinding of cut-oli relay 202 and the upper winding of cut-oil relay HBS, which is now reconnected to the C lead through contacts of the restored release relay |02. lt may be'pointed out that cut-off relay |00 normally does not operate when a connection is cleared out,

as the ground potential is usually reinovedirom the C lead at the linder'connector link by the time release relay |02 restores and reconnects the up- 'Zi per winding of relay |00 to the C lead.

relay is next opened by line relay. Resistor H4, Y of va. relatively high value, reduces sparking at the Y.

A reverting call inbefore referred to, when the subscriber on a rural line desires to' conversewith another subscriber on the same line he calls the directory n-umber of the desired subscriber, with the result that the connector in use attempts tomake connection with the calling line but iinds it busy and impresses a busy tone signal on the calling line in the usual manner. Upon hearing this signal, the calling subscriber replaces his receiver, whereupon the connector (responsive to a circuit closed from the C wiper |83 of the connector,

' over the C lead of the called line, to the C wiper of the finder) signals the called subscriber by sending Vout his ringing code, following which the Vtwo Vsubscribers remove their receivers and converse, while the exchange apparatus is released and the r-ural line is held guarded from the line circuit.

' The way in which the rural line repeater RLR, Fig. l, participates in the makingof a reverting call as outlinedabove will now be pointed out more particularly.

The action resulting .from the removal of the receiver at the calling station and from the` dialling of the desired number are as described hereinbefore. It will be recalled that relays |0|-|03, |05, |09, and H0 are energized after the num,- ber has been called,.while cut-in relay |07 has been energized or not depending upon the result of the resistance test made by the marginal test relay |05. ofi and lockout relays 202 and 203 are in energized condition in the line circuit LC, and that the I Clead of the calling line is extended through the As explained in my prior Patent 1,999,788, here- It will be recalled also that the cutline circuit'to the finder-'connector link which finder connector link maybe assumed to be the one illustrated in part. Now, when the wipers |82, |85, and |83 of the connector encounter the negative, positive, .and C leadsof the calling line, because of the grounded condition of the C lead, the C wiper |83 of the connector encounters ground potential and the connector therefore sends back the usual busy-tone signal to `the calling line. The calling subscriber now replaces his receiver, whereupon relays |0|, H0, |09, |02, and |03 restore in the order named, thereby clearing out the repeater RLR. At this time the connector C and the finder F do not restore responsive to the opening of the control circuit at the upper contacts of repeating relay I0; ground potential is therefore maintained on the C lead. At the time release relay |02 restores it reconnects the upperwinding of the electro-polarized cutoff relay 00 to the C lead, through resistor ll'l, and it vinserts the lower winding of relay |00 in series with the C lead, whereby current ilows momentarily through the lower winding of the relay to enable the Cconductor to be tested as to the direction of current-flow thereover. At

' this time, with ground potential applied to the C conductor by wiper |83 of the connector current flow over the C lead passes to the negative pole of the exchange battery through cut-off relay 202. The direction of current-flow through the lower winding of cut-off relay |00 is and recloses the shunt around the lower winding of relay |00, terminating the polarity test.

The negative and positive conductors of the called line are now cleared for the application of ringing current.

When the two subscribers remove their re- Y ceivers after the ringing operation, they may converse with each other over the line RL.l The finder-connector link is cleared out by the operation of cutting oi the ringing current when the called subscriber replies, thereby removing ground potential from the C conductor of the line RL and the C conductor of the line circuit LC. When this occurs, cut-off relay H10-of the repeater RLR and cut off relay 202 oitheline circuit LC both restore. The repeater RLR is thereby again connected to the line RL, and the line relay 20| is again bridged across the associated talking conductors of the line circuit. Relays |0I, H0, and |09 reoperate in the repeater RLR, and at the same time release and auxiliary relays |02 and |03 operate responsive to the operation of line relay I0|. Cut-oir relay |00- is disconnected upon the operation of release relay |02,

In the line circuit LC, line relay 20| energizes responsive to the energization `or repeating relay ||0 of the repeater. RLR. It. grounds the C lead to mark the line busy'to the connectors. At this time the slow-releasing lockout relay 203 is still in operated condition because it has been held operated by the now restored cut-oir relay 202.

Under this condition, when line relay 20| operates it closes a locking circuit for lock-out relay 203 to maintain it operated and .thereby prevent the grounding of start conductor 205 at the same time. With lock-out relay 203 operated and cutoff relay 202 restored, the associated C conductor which extends to the bank oi the finder F and the other iinders is maintained disconnected from the winding of cut-off relay 202; therefore the line circuit LC is not marked calling in the bank of the finder F, whereby the nding of the line circuit LC by a finder started from some other line is prevented.

When the subscribers on the line RL have finished their conversation and replaced their receivers, the repeater RLR clears out as before pointed out, and line relay 20| in the line circuit LC restores when its circuit is opened at the contacts of repeating relay H0. Lock-out relay 203 restores when its circuit is opened by line relay 20|. The circuit equipment associated with the line RL is thereby returned to its normal condition.

Outgoing toZl calls The way in which the rural-line repeater RLR n functions in an outgoing toll call to avoid an inadvertent operation of cut-off relay |00 will now be explained.

It is a standard requirement in an automatic telephone system that, when connection is extended through the automatic switching apparatus to a toll switchboard, the connection established through the automatic switching apparatusrbe held subject to disconnection on the part of the operator at the toll switchboard, which arrangement permits the calling automatic subscriber to ash the operator Yat the toll switchboard by moving his switchhook 'in the usual manner. It was explained in my prior patent before referred to that the finder connector link is held when a connection is extended to a manual switchboard, and that the nder maintains ground potential on the C conductor of the calling n purpose.

line in order to maintain the cut-ofi relay operated in the line circuit'associatedwith the calling line; Assume now that the illustrated link has been operated to extenda connection fromvthe rural line RL by way of the connector C to a tollswitchboard by way of trunk equipment as illustrated in the prior patent, ground potential maintained on the C lead of the line circuit LC by the iinder F under the control of a switchboard operator, and the connection is therefore not released in the event that the bridge is openedron the calling line. It

may be assumed nowthat the calling subscriber desires to recall the toll Voperator and that he depresses hisv u When the switchhook is depressed, the relays iiii and i l0 restore to secure the signalling of the operator, responsive to the opening o'the upper contacts of repeating relay H0. If the switchhook is depressed longerthan momentarily,-

release relay |02 also restores, as in thecase when a calling subscriber Nreplaces hisreceiver at the end of conversation. When it restores, release relay |02 reconnects the upper winding of cut-oirc relay 00 to the associated C lead, as in a normal clearing out operation'. At this time, relay |00 must not be permitted to operate, for it would disconnectthe line from the rep-eater andthereby open the talking circuit if permitted to operate. The operation of relay |00 is prevented at this time by the ilow of current in an opposing direcf.

tion in the lower winding of .therelay The two windings of relay |00 are in series, with relay |02Y restored' and with` the slow releasing auxiliaryrelease relay |03 still operated, for ground potential is applied by the nder F to the C lead by way` oi the line circuit LC. The current-flow through the lower winding of relay |00 is in reverse direction with respect to the current that flows through this winding when the receiver is replaced to permit ringing in a reverting call, as at that time ground potential is supplied to the C lead of the line RL at the left-hand C terminal of repeater RLR by the connector instead of by way of the line circuit and a iinder as it now is. The releasing time of auxiliary release relay |03 is'4 adjusted Y so that relay |03 does not restore following the switchhook one or more times forltl'iis f restoration of relay |02 in normal recallingfas y the switchhook is then'depress'ed each time for only an instant. Y

When the hookswitch is again permitted to rise vand the line circuit is again closed, relays i0 I, i i0,

and |00 reoperate, and relay |02 reoperates'responsive to the operation of relay lili, again removing the lower winding `of relay |00 from the circuit and disconnecting the upper winding of the relay. The flashing signalto the operator is relay I0.

In the event that the calling subscriber holdsthe terminated at the upper contacts of the repeating hook switch down too long or replaces his receiver during a call to the toll switchboard, the restoration kof auxiliary release relay |03 recloses the shunt around the lower winding of nelectropolarized relay |00, permitting relay |00 lto operate vresponsive to current flow in its upper winding. y H A It may be here pointed out that release relay |02 is adjusted to restore in about the same time required for the release relay of a finder-connector link to restore so as to reconnect cut-oii relay i0@ in a reverting call and permit it toreoperate and clear the line by the time the ring-back operation has started responsive .to the restoration .of the release relay in the link; f

In the event that it is desired that cut-off relay l 00 be not permitted to operate even though the calling subscriber replaces his receiver in a call to the toll switchboard, the free terminal of the winding of auxiliary release relay 103 may be disconnected from the armature of release relay l02 and connected to the associated C lead, in which case auxiliary release relay |03 does not fall back responsive to the restoration of release relay |02, but remains operated as long as ground potential is maintained on the C lead, thereby Ymaintaining the lower winding of relay |00 in circuit to preventoperation of the cutoff relay. With this arrangement, a subscriber who has-called the toll operator will not be-v come disconnected during hashing in the event that he inadvertently holds the switchhook down Y longer than isnormally intended.

What is claimed is: 1. In an automatic telephone system, a subscriber line, calling terminals individual to said line, an impulse repeater inserted between saidY ing the line from seizure by way of said called terminals when Va call is originated thereover, and means for preventing the operation of the said cut-01T relay when a call is originated over the line and the line is guarded from seizure through the called terminals thereof.

2. In an automatic telephone system wherein the operation of the automatic switches in testing lines is controlled over 'a third or control conductor according to potentials impressed thereon, a subscriber line having individual called terminals and individual calling terminals, the said called terminals being associated directly with the line, an impulse repeater inserted in the line between the called terminals and the calling terminals of the line, a control conductor included in the repeater, and means elective when a call is originated on said line for joining the control terminal in the group of calling terminals to the control terminal in the groupV of called terminals by way of said control conductor. Y Y

3. In an automatic telephone system, a subscriber line having individual called terminals and Calling terminals, the said called terminals being directly associated with the line, line equipment associated with the calling terminals, an impulse repeater inserted in the line between the called terminals and the calling terminals theref of, means associated with said called terminals for disconnecting said line from said repeater when said line is called,.and a control conductor extending from the line circuit associated with the calling terminals through said repeater to the'called terminals of the line to Vcarry guia-rding Ypotential between the calling and called terminals of the line.

4. In an automatic telephone system, a subscriber line having called and calling terminals,

an impulse repeater interposed between the called the line for disconnecting the4 cut-oil? relay" to avoid its operation when guarding potential is placed o n the called terminals of the line, and

Vmeans effective when a connection has been set up which is held from the called end thereof for preventing operation of the cut-olf relay when it is reconnected during switchhook signalling periods.

5. In an automatictelephone system, a scriber line having called terminals connected Y thereto and calling terminals associated there with, an impulse repeater'interposed in the said line between the called ,and calling terminals thereof to .repeat switch operating impulses'in calls originating on the same line, a cut-orf relay operable over the usual control conductor associated with the said terminals of the line to disconnect theY repeater when the line is called,

circuit arrangements effective in one type of .call y which can be set up from said line for enabling the calling subscriber to signalover the-established connection by operating his switchhook, a second polarizing windingincluded in said `cutoff relay to prevent operation thereof when Yen'er- 3b gized, and means for inserting said polarizing winding in circuitduring the switchhook signalling operation to-prevent operation of the vsaid cut-olf relay. v

6. In an impulse repeater, a line relay, a repeating relay, and a timer relay, means `Afor energizing the repeating relay depending upon the energization of the line relay, Ymeans for energizing the timing relay dependent upon Athe energization of the repeating relay, said timing vrelay being slow releasing to Yinsure the repeating of an impulse of minimum length, and circuit arrangements controlled jointly by the timer relay and said repeating relay for preventing the re- Voperation of the repeating relay followingfthe restoration thereof until the timerrelay has restored, and impulse repeating contacts on said vrepeating relay'to repeat open-circuit impulses received by said line relay.

7. In combination, an impulse repeater including a line relay having contacts for repeating operable when the f" circuit of the line relay is ,closed over a circuit Y of relatively low resistance, and means associated with said marginal test relay effective when the test relay operates to insert a resistanceelementy in the circuit of the line relay to compensate for the relatively low resistance of the circuit over which it is taken for use.

8. In combination, an impulse repeater including a line relay having contactsfor repeating received impulses, means for energizing said line relay and for delivering impulses to it `over circuits of various resistances, a marginal testrelay in circuit with said line relay operable when 4the circuit-of Vthe line relay is closed over a circuit of relatively vlow resistance, and means associated with said marginal test relay effective when the test relay operates to adapt the-repeater to -repeat impulses received over the low resistance circuit. Y

- 9. In combinatioman impulse repeater including a line relay comprising means for repeating test relay and effective when the test relay op-V received impulses, circuits of various impedances crates for adapting the repeater to repeat imadapted to deliver control impulses to said line pulses received over circutsrhaving impedances relay, a marginal Jtest relay operable when the different, in said one sense, from said predeter- 5 impedance of the circuit to said line relay is mined value. Y

diierent, in one sense, from a predetermined NORMAN H. SAUNDERS. value, and means associated with said marginal 

